Manufacturers of jet transport aircraft often develop families of aircraft which are derived from an original base model. This approach reduces manufacturing and development costs through the use of common parts and assemblies. Typically, the derivative models are more economical and profitable to operate because of growth in passenger capacity.
Although most growth in passenger capacity comes from stretching the fuselage, it would also be advantageous in some instances to increase passenger capacity (and/or fuel capacity, cargo capacity, etc.) by increasing the wing area. Conventional aircraft wing structures, however, are not easily modified to increase the wing area. This is unfortunate because wing growth may, in fact, offer a broader range of aircraft size options (i.e., gross weights) than fuselage growth.
The primary structure of conventional jet transport wings is typically manufactured from aluminum and other metals. This type of structure can be extremely labor intensive to build because many of the components are essentially handmade, custom parts that are unique to a particular aircraft model. A related consequence of this is that the assembly of these parts is often unique to the particular aircraft model as well. These factors make it difficult to economically develop a family of aircraft wings based on an original model.